1. Field of the Invention
The present invention relates to a refrigerant compressor for compressing a refrigerant or coolant and a refrigeration or cooling system incorporating same, for use in, such as, an electric refrigerator and a car air conditioner.
2. Description of the Prior Art
Recently, in consideration of the environmental pollution and, particularly, the ozone destruction and the global warming, the use of the chlorine-containing freon (chlorofluorocarbons abbreviated as CFC) has been seriously discussed and is going to be regulated worldwidely.
The freon to be regulated includes the chlorine-containing freon, such as, the freon 11, the freon 12, the freon 113, the freon 114 and the freon 115. As a result, the freon 12 which has been widely used as a refrigerant in the refrigeration system incorporated in, such as, the refrigerator and the dehumidifier is also to be regulated.
In the circumstances, a refrigerant which can be a substitute for the freon 12 has been an immediate need, and various kinds of compounds have been researched. Among them, carbon hydride fluoride has been highlighted as an alternate refrigerant for the freon 12 because of its low reactivity with ozone and its short decomposition time in the atmosphere. Particularly, the freon 134a (1, 1, 1-tetrafluoroethane, CH.sub.2 FCF.sub.2) is known to have prevailing properties. For example, an ozone destruction parameter (ODP)of the freon 134a is 0 (zero) when that of the freon 12 (dichlorodifluoromethane, CCl.sub.2 F.sub.2) is assumed to be 1, and further, a global warming parameter (GWP) of the freon 134a is no more than 0.3 when that of the freon 12 is assumed to be 1. Accordingly, the freon 134a less affects the global environment and is, in addition, noncombustible. Still further, thermal properties, such as, temperature-pressure characteristics of the freon 134a are close to those of the freon 12 so that the refrigeration system of, such as, the refrigerator and the dehumidifier and its refrigerant compressor which have been using the freon 12 can be used without largely modifying their structure. As a result, the freon 134a has been prevailing as a substitute for the freon 12.
As is known, the hermetic refrigerant compressor widely employed in, such as, the refrigerator uses an lubricating oil which is filled in a sealed casing of the refrigerant compressor for lubricating its internal compressing unit. This lubricating oil is required to have mutual solubility with the refrigerant so as to ensure the effective recovery of the lubricating oil into the sealed casing. In this respect, the conventional refrigeration system using the freon 12 has been using the mineral oil or the alkylbenzene oil as lubricant.
However, a chemical structure of the freon 134a is so special that the conventional lubricating oil containing the mineral oil or the alkylbenzene oil as a main component can not be used as lubricant on a practical basis due to its poor solubility with the freon 134a.
In order to overcome this problem, researches were made to attain lubricating oils from known materials having solubility with the freon 134a. However, none of them could satisfy the required properties in view of, such as, lubricity, friction resistance and abrasion resistance for sliding parts of the compressor and in view of influence to electrical insulators and desiccants in the refrigeration system.
Further researches have been made for the lubricating oil which has solubility with the freon 134a and, in addition, which has practical insulation, lubrication and hygroscopic properties, and finally developed ester lubricating oils for the hydrogen-containing freon refrigerants as disclosed in, such as, Japanese First (unexamined) Patent Publications Nos. 3-128991 and 3-128992. As a result of this, the carbon hydride fluoride refrigerants as represented by the freon 134a have become practical for use in the refrigeration system.
On the other hand, no substantial improvement has been made in machine parts of the refrigerant compressor and the refrigeration system for using the carbon hydride fluoride refrigerant.
Hereinbelow, conventional refrigerant compressors and refrigeration systems will be described with reference to the accompanying drawings.
FIG. 17 is a systematic diagram showing a schematic structure of a typical conventional refrigeration system as disclosed in Japanese First (unexamined) Patent Publication No. 62-200157.
The typical conventional refrigeration system includes a refrigerant compressor 1, a condenser 2, a drier 3 incorporating a water adsorber, such as, a molecular sieve and a metal screen filter of about a 150 mesh size, an expansion mechanism 4 with an expansion valve in the form of a capillary tube and an evaporator 5, which are hermetically connected by piping as shown in FIG. 17. The refrigerant and the lubricating oil are enclosed in the refrigeration system for circulation in a direction of an arrow as indicated in FIG. 17.
As the refrigerant compressor 1 employed in the refrigeration system, there are available various kinds of compressors selectable depending on intended use of the refrigeration system.
FIG. 18 is a sectional view showing a typical conventional reciprocating refrigerant compressor. This type of the compressor is disclosed in, such as, Japanese First (unexamined) Patent Publication No. 3-290073. In FIG. 18, the compressor includes a sealed casing 6 which incorporates therein a motor 7 and a reciprocating compressing unit 9. In the compressor, the refrigerant gas circulated from the evaporator is introduced into the sealed casing 6 via an induction pipe 10 and then released into an induction muffler 12. The refrigerant gas is then sucked into an intake tube 14 and further introduced into a cylinder of the compressing unit 9.
In the conventional reciprocating refrigerant compressor, no filter is provided in a refrigerant inflow passage from the induction pipe 10 to the cylinder.
The refrigerant gas introduced into the cylinder is then compressed and flows out through a discharge muffler 15.
FIG. 19 is a sectional view showing the discharge muffler 15. The discharge muffler 15 includes a baffle 17 in a muffler chamber 20. The refrigerant gas compressed by the compressing unit 9 is released into the muffler chamber 20 via a discharge hole 18, and then flows into a discharge pipe line 25 passing an annular gap 22 between the baffle 17 and a mounting bolt 21. The refrigerant gas is then guided to exterior of the sealed casing 6 via the discharge pipe line 25.
In the conventional reciprocating refrigerant compressor, no filter is provided in a refrigerant discharge passage from the cylinder of the compressing unit 9 to the exterior of the sealed casing 6.
FIG. 20 is a sectional view showing a typical conventional rotary refrigerant compressor. This type of the compressor is disclosed in, such as, Japanese Second (examined) Patent Publication No. 61-47994. In FIG. 20, the compressor includes a sealed casing 31 which incorporates therein a motor 34 formed by a rotor 32 and a stator 33, a rotating shaft 35 firmly fitted through the rotor 32 and a compressing unit 36 operatively coupled to the motor 34 via the rotating shaft 35. In the compressor, the refrigerant gas circulated from the evaporator is released into an induction muffler 28 via an induction pipe 27 and passes through a metal screen filter 29 of a 150 mesh size provided in the induction muffler 28 so as to be introduced into a cylinder 37 (FIG. 21).
As shown in FIG. 21, the refrigerant gas compressed by means of the cylinder 37, a roller 38 and vanes 39 of the compressing unit 36 is discharged into a space within the sealed casing 31 via a discharge muffler 40 as indicated by arrows in FIG. 21. The refrigerant gas is then discharged into the exterior via a discharge pipe 26 mounted to the sealed casing 31.
In the conventional rotary refrigerant compressor, no filter is provided in a refrigerant discharge passage from the cylinder 37 to the exterior of the sealed casing 31.
FIG. 22 is a sectional view showing a typical conventional refrigerant compressor of a car air conditioner. This type of the compressor is disclosed in, such as, Japanese First (unexamined) Patent Publication No. 2-153274. In FIG. 22, the compressor includes a main casing 41 incorporating therein a refrigerant gas compressing section driven by a drive mechanism 43 which is driven by rotation of a rotating shaft 42. To the main casing 41, a block is integrally mounted which includes therein an induction section for feeding the refrigerant to the compressing section and a discharge section for discharging the refrigerant compressed by the compressing section.
Specifically, the refrigerant gas is sucked into a cylinder 45 via an induction muffler 48 provided in the induction section and then compressed due to a reciprocating motion of a piston 44 in the cylinder 45.
In the conventional refrigerant compressor of the car air conditioner, no filter is provided in a refrigerant induction passage from the exterior to the cylinder 45.
The refrigerant gas compressed in the cylinder 45 is discharged into the exterior of the compressor after a temporal stay in the discharge muffler 47.
In the conventional refrigerant compressor of the car air conditioner, no filter is provided in a refrigerant discharge passage from the cylinder 45 to the exterior of the compressor, either.
As aforementioned, the lubricating oils for the freon 134a as disclosed in, such as, Japanese First (unexamined) Patent Publications Nos. 3-128991 and 3-128992 are the ester oils. Accordingly, there has been raised another problem that the ester oils dissolve rubber and resin. As a result, when using the ester lubricating oil, a certain design modification was necessary for rubber and resin parts in the refrigerant compressor to be resistible against dissolution by the ester lubricating oil.
In the circumstances, the present inventors have changed a coating material for a motor coil in the compressor to polyamide imide and a motor insulation film to a crystalline film of polyethylene terephthalate having a glass-transition temperature higher than the conventional film, and further removed a NBR (butadieneacrylonitrile rubber) member of a damping strap provided in the compressor. In this condition, the freon 134a refrigerant and the lubricating oil containing ester as a main component were filled into the compressor, and a test working of the refrigeration system including this compressor was performed. The result was that no short circuit of the motor, no insulation failure or the like occurred.
However, in the foregoing refrigeration system, there has been raised another serious problem that a cooling power of the refrigeration system became much lower than expectation. The reason for this was found as follows:
During production processes of the compressor and the evaporator, the mineral oil and a solvent are respectively used so that these organic substances, i.e. fats and oils and the like remain inside the refrigeration system. The lubricating oil containing ester as a main component dissolves these organic substances to produce contaminants. These contaminants block or deteriorate the flow of the refrigerant in the capillary tube so as to lower the cooling power or effect of the refrigeration system.
In the circumstances, component parts of the refrigeration system were fully washed using a solvent or a surface active agent, and then the ester oil was filled in. As a result, an amount of the generated contaminants was reduced. Specifically, an amount of the generated contaminants was 0.005 grams when measured after a six-month operation of the refrigerator of 400 liters which incorporates the refrigeration system having the reciprocating refrigerant compressor with a cylinder capacity of 7.7 cm.sup.3.
However, the generation of the contaminants in the refrigeration system could not be prevented completely however carefully the component parts of the refrigeration system were washed. Although only a slight amount of the contaminants was generated after the washing, the generated contaminants adversely affect a flow resistance in the capillary tube to an extreme degree to increase the flow resistance of the capillary tube by 10% to 20%. As a result, the lowering of the cooling power could not be avoided in the conventional refrigeration system using the carbon hydride fluoride refrigerant and thus the ester lubricating oil.
This means that the conventional filter, such as, the metal screen filter of about a 150 mesh size can not catch or capture the contaminants generated due to the dissolution of the organic substances by the ester lubricating oil.